Aerodynamics

Effect of carrier particle shape on dry powder inhaler performance

by Waseem Kaialy

Aerodynamics of pollen grains involved in sampling efficiency. Abstract Index Conclusions. Thesis by Diego Fernandez-Sevilla

by Diego Fdez-Sevilla

Supervised by Prof. Jean Emberlin 8Worcester Uni.) and Dr. Eckart Schultz (DWD).

Aerobiology studies the passive transport of biological particles in the air. It has many applications including... more Aerobiology studies the passive transport of biological particles in the air. It has many applications including allergy (e.g. hayfever and asthma), crop pollination, forestry, horticulture, and biodeterioration. A central theme is the requirement for detailed information about the residence time of atmospheric particles, which is highly dependent on their settling velocity. This basic parameter is directly related to the aerodynamic behaviour of the pollen grains. It is an essential component for modelling dispersal and atmospheric transport, and it is of special interest for pollen forecasting and transgene escape from genetically modified crops. The sampling efficiency of the sampling methods relies on removing pollen grains from the airflow stream-lines, so differences in aerodynamic behaviour between pollen types could lead to disproportionate representation in the pollen count under variable methodological conditions. Reliable data on real-world pollen settling velocities are needed as little attention has been given to this topic and reported values differ considerably. This research investigates pollen settling velocities in wind tunnel and outdoor experiments, and calculates them from combining deposition and concentration measurement with standard equipment and in different meteorological conditions. For this purpose pollen grains have been sampled in parallel and counted on different sampling media such as impaction surfaces (Hirst-type volumetric trap), deposition plates (Sigma-2 sedimentation sampler) and glass fibre filters (standard particle samplers). Results obtained in this investigation prove that pollen types with different aerodynamic properties express significant differences in their aerodynamic behaviour in following stream-lines. This suggests that, if distortions in the streamlines exist for any kind of pollen sampling method, differences in settling velocity between pollen types could lead to disproportionate representation of certain pollen types under certain meteorological conditions of wind speed and particle settling velocity. Also, results obtained show a negative relationship between atmospheric conditions of vapour pressure deficit (VPD) and pollen settling velocity.Accordingly, atmospheric conditions of VPD have the potential to define the aerodynamic behaviour of the pollen grains. This finding has implications not only in characterising atmospheric conditions for pollen transport but also for airborne pollen sampling. The results obtained in this thesis have applications for further research concerning key areas of the science such as the application of correction factors on the pollen counts obtained, pollen transport modelling and the assessment of factors defining the structure of the pollen cloud.

Positivity-preserving High-resolution Schemes for Systems of Conservation Laws

by Bernard Parent

A new class of flux-limited schemes for systems of conservation laws is presented that is both high-resolution and... more A new class of flux-limited schemes for systems of conservation laws is presented that is both high-resolution and positivity-preserving. The schemes are obtained by extending the Steger-Warming method to second-order accuracy through the use of component-wise TVD flux limiters while ensuring that the coefficients of the discretization equation are positive. A coefficient is considered positive if it has all-positive eigenvalues and has the same eigenvectors as those of the convective flux Jacobian evaluated at the corresponding node. For certain systems of conservation laws, such as the Euler equations for instance, this condition is sufficient to guarantee positivity-preservation. The method proposed is advantaged over previous positivity-preserving flux-limited schemes by being capable to capture with high resolution all wave types (including contact discontinuities, shocks, and expansion fans). Several test cases are considered in which the Euler equations in generalized curvilinear coordinates are solved in 1D, 2D, and 3D. The test cases confirm that the proposed schemes are positivity-preserving while not being significantly more dissipative than the conventional TVD methods. The schemes are written in general matrix form and can be used to solve other systems of conservation laws, as long as they are homogeneous of degree one.

Ambipolar Diffusion and Drift in Computational Weakly-Ionized Plasmadynamics

by Bernard Parent

Modeling of ambipolar diffusion and drift taking place within a weakly-ionized fluid can lead to some convergence... more Modeling of ambipolar diffusion and drift taking place within a weakly-ionized fluid can lead to some convergence difficulties when the ion conservation equation and the electric field potential equation are solved consecutively. A novel formulation of the ion flow rate is proposed here that reduces the computing effort to reach convergence by a factor of 10 or more. It is shown that by recasting the ion flow rate in terms of drift and ambipolar diffusion components, the sensitivity to the electric field is reduced hence alleviating the stiffness of the system of equations and permitting significantly faster convergence. What makes the method particularly appealing is that (i) it yields faster convergence without affecting the accuracy of the converged solution and (ii) it is not restricted to specific discretization or relaxation schemes and can hence be readily implemented in existing flow solvers. Because it is developed in general form ({\it i.e.}\ applicable to a multicomponent plasma in the simultaneous presence of electric current and magnetic and electric fields), the method is notably well-suited to simulate ambipolar diffusion within ionized multi-species flow solvers and is recommended for all flowfields as long as the plasma remains weakly-ionized and quasi-neutral.

Development and validation of a high order numerical solver for cross-flow turbine hydrodynamics

by Esteban Ferrer

E Ferrer and RHJ Willden, In Proceedings 9h European Wave and Tidal Energy Conference (EWTEC-2011), September 2011, Southampton (UK)

We present a newly developed unstructured highorder
h/p Discontinuous Galerkin Finite Element solver forthe... more We present a newly developed unstructured highorder
h/p Discontinuous Galerkin Finite Element solver forthe computation of tidal turbine hydrodynamics. The solverallows for accurate flow solutions of the two dimensional incom-pressible Navier-Stokes equations on hybrid meshes (triangular-quadrilateral) with rotating geometries using sliding mesh in-terfaces. High accuracy is obtained by enabling arbitrary poly-nomial orders within each mesh element allowing mesh sizerefinement (h-refinement) and/or polynomial enrichment (p
-refinement).The solver is validated for static NACA0012 and NACA0015airfoil flows for a range of Reynolds numbers including laminarand turbulent regimes. Results for a typical cross-flow tidalturbine are also included for laminar flows and the resulting flowphysics explored. Wake-blade interference effects are analysedfor single and three bladed turbines. Results for a three bladedturbine under ducted conditions (tidal fence concept) are alsoreported.We show that the solver provides accurate results and is thus avaluable tool to accurately predict flows through cross-flow tidalturbine devices and to explore their hydrodynamics.

CFD predictions of transition and distributed roughness over a wind turbine airfoil

by Esteban Ferrer

E Ferrer and X Munduate, 47th AIAA Aerospace Sciences Meeting, January 2009

Simplified wind flow and aerodynamic response of residential homes: Laboratory and Computational Fluid Dynamics simulations

by Aly Mousaad Aly Sayed Ahmed

Tuan-Chun Fu, Aly Mousaad Aly, Arindam Gan Chowdhury, Girma Bitsuamlak, DongHun Yeo, and Emil Simiu

4th International Conference on Experimental Vibration Analysis for Civil Engineering Structures (EVACES 2011), 3-5 October 2011, Varenna (Lecco), Italy (2011).

The reliable measurement of pressures on low-rise buildings in the atmospheric boundary layer (ABL) flow remains a... more The reliable measurement of pressures on low-rise buildings in the atmospheric boundary layer (ABL) flow remains a challenge, as has been shown by the large discrepancies among results obtained in different wind tunnel facilities or even in the same wind tunnel. Two major causes of the discrepancies are the difficulty of simulating low-frequency turbulent fluctuations uniformly across laboratories, and the small scale of models in typical civil engineering wind tunnels. To address these issues, it was proposed that a simplified flow be used in laboratory simulations, rather than a conventional ABL flow. In the simplified flow the reference mean wind speed is larger than the mean wind speed of the ABL flow, and the low- frequency fluctuations present in the ABL flow are suppressed; that is, the peak energy of the missing low-frequency fluctuations is supplied in the simplified flow by the increment in the mean wind speed, which may be regarded as a flow fluctuation with zero frequency. High-frequency turbulent fluctuations, which typically affect flow reattachment, are approximately the same in the ABL and the simplified flow. Since, over small distances, low-frequency fluctuations are highly coherent spatially, the peak aerodynamic effects of the two flows may be hypothesized to be approximately the same. Preliminary experimental results obtained in Florida International University’s small-scale Wall of Wind facility are shown to support this hypothesis. The implications of our hypothesis for Computational Fluid Dynamics (CFD) simulations are briefly discussed. It is submitted that the detailed simulation of the turbulence in the oncoming ABL flow appears to be typically unnecessary for the testing of residential homes and other structures with relatively small dimensions. The use of simplified flows is advantageous from the points of view of model scaling, measurement accuracy, and repeatability of the testing; for CFD calculations it is advantageous from the standpoint of efficiency. The possibility of extending the proposed approach to achieve approximate numerical simulations of pressures on buildings with any dimensions, including tall buildings, is also briefly discussed.

Influence of Inflow Models on Helicopter Aeroelastic Optimization

by Ranjan Ganguli

Murugan, S., and Ganguli, R., “Influence of Inflow Models on Helicopter Aeroelastic Optimization”, Computational Fluid Dynamics Journal, Vol. 16, No. 2, 2008, pp. 444-453.

Helicopter Blade Flapping With and Without Small Angle Assumption in the Presence of Dynamic Stall

by Ranjan Ganguli

Effect of Uncertainty on Helicopter Performance Predictions

by Ranjan Ganguli

Rotorcraft Parameter Estimation from Real Time Flight Data

by Ranjan Ganguli

Phonetic implementation of nasality in Taiwanese (and French): Aerodynamic case studies

by Feng-fan Hsieh

Chang, Yueh-chin, Feng-fan Hsieh and Yu-lun Hsieh. 2011. Phonetic implementation of nasality in Taiwanese (and French): Aerodynamic case studies. In Wai-Sum Lee and Eric Zee (eds.), Proceedings of the 17th International Conference of Phonetic Sciences, pp. 436-439.

This paper aims at systematically investigating the aerodynamics of nasalization in Taiwanese, a language that has a... more This paper aims at systematically investigating the aerodynamics of nasalization in Taiwanese, a language that has a nasality contrast in its vowels but are subject to stricter restrictions on nasality distribution than French. Our results show that i) the onset consonantal effects on nasal anticipatory coarticulation are subtly different between the two languages; in particular, voiced stops avoid nasal contexts in Taiwanese, ii) in onset positions, aspirated stops and fricatives induce more nasal coarticulation, iii) coda [n] triggers the least anticipatory vowel nasalization in both languages, iv) the production of nasal vowels are generally the same and vowel height is positively correlated with nasalization in both languages, v) that French has more nasal airflow volume than Taiwanese does, but no significant difference could be found as far as nasal airflow duration is concerned. Taken together, our results confirm that phonological patterning does have a bearing on phonetic implementation.

Simulation of Vehicle Aerodynamics Using a Vortex Element Method

by Philippe Chatelain

Goéric Daeninck, Philippe Chatelain, Michael Rubel, Grégoire Winckelmans and Anthony Leonard, The aerodynamics of heavy vehicles: trucks, buses and trains, Lecture notes in applied and computational mechanics 19 (2004).

Science and cycling: current knowledge and future directions for research

by Louis Passfield